"Didn’t you hear about ... the kids who tried to steal Gryffindor’s sword out of Snape’s office at Hogwarts? ... One of the kids who tried to take the sword was Bill’s younger sister. She and a couple of friends got into Snape’s office and smashed open the glass case where he was apparently keeping the sword. Snape caught them as they were trying to smuggle it down the staircase."
-- Dirk Cresswell (DH15)

During the fall of 1997, Neville, Ginny, and Luna are the leaders of the anti-Death Eater group of students at Hogwarts. At one point, probably during October, the three of them try to steal the Sword of Gryffindor out of the Headmaster’s office. They are caught, however, and given detention with Hagrid in the Forbidden Forest. Harry, Ron, and Hermione hear about the incident from the portrait of Phineas Nigellus which Hermione has stashed in her handbag (DH15).

Commentary

Pensieve (Comments)

This doesn’t contain all of the information? The story spread was that they were “punished, and cruelly”; but in reality they were given detention with Hagrid in the Forbidden Forest. All of this is in DH 15.